1. Field of the Invention
This invention relates to a circularly polarized wave generator for transmitting circularly polarized electromagnetic and a circularly polarized wave receiving antenna for receiving the circularly polarized electromagnetic waves.
2. Description of the Related Art
Such circularly polarized wave generator and circularly polarized wave receiving antenna is shown for example in FIGS. 1 and 2. The circularly polarized wave generator and circularly polarized wave receiving antenna shown in FIGS. 1 and 2 includes a cylindrical waveguide 102, a linear receiving bar 101 inserted through the wall of the proximal part of the waveguide 102 at a right angle thereto, and a dielectric plate 103 arranged within the waveguide 102. The dielectric plate 103 is a flat plate having a width equal to the inner diameter of the waveguide 102 and placed with its longitudinal axis in alignment with the axis of the waveguide 102.
A circularly polarized wave is incident on the receiving antenna at an open distal end of the waveguide 102 from the direction shown by arrow e in FIG. 2. The field amplitude component of the circularly polarized wave perpendicular to the major surface of the dielectric plate 103 is transmitted through the waveguide 102 without being affected by the dielectric plate 103 to reach the reception bar 101. The field amplitude component of the circularly polarized wave parallel to the major surface of the dielectric plate 103 is retarded by being transmitted through the dielectric plate 103 to reach reception bar 101. The field amplitude component or the circularly polarized wave transmitted through the dielectric plate 103 is delayed by 1/4.lambda. where .lambda. represents wavelength, when it reaches the reception bar 101. The result is that the field amplitude components of the circularly polarized wave perpendicular and parallel to the major surface of the dielectric plate 103 reach the reception bar 101 simultaneously so as to be outputted via reception bar 101 as reception signals.
It is noted that, if the electromagnetic waves are transmitted via reception bar 101, the circularly polarized wave receiving antenna may be used as a circularly polarized wave generator for transmitting circularly polarized wave at the distal end of the waveguide 102 by the operation of the dielectric plate 103.
Also known in the field is a circularly polarized wave reception antenna made up of a cylindrically-shaped waveguide 102 and a pair of reception bars 104a, 104b inserted through the wall of the waveguide 102 in a direction perpendicular to the axis of the waveguide, as shown in FIGS. 3 and 4. The reception bars 104a, 104b are arranged at right angles to each other and have their distal ends in the vicinity of the axis of the waveguide 102. These reception bars 104a, 104b have their proximal sides connected to each other via a synthesizer 105 and to a reception signal output end 104. The synthesizer 105 is designed so that the distance from the reception bar 104a to the output terminal 104 is longer by 1/4.lambda. than the distance from the other reception bar 104b to the output terminal 104.
In the present circularly polarized wave reception antenna, the circularly polarized wave is incident on the open distal end of the waveguide 102 from the direction shown by arrow e in FIG. 4. The reception bar 104a receives field amplitude components parallel to the axis of the reception bar 104a to transmit the components via synthesizer 105 to the reception signal output terminal 104. The other reception bar 104b receives field amplitude components parallel to the axis of the reception bar 104b to transmit the components via synthesizer 105 to the reception signal output terminal 104. The field amplitude components received by the reception bar 104a on reaching the output end 104 is delayed by synthesizer 105 by 1/4.lambda. with respect to the field amplitude component received by the other reception bar 104b. The result is that the field amplitude components of the circularly polarized wave parallel to the axes of the reception bars 104a, 104b reach the reception signal output terminal 104 simultaneously so as to be outputted via reception signal output terminal 104 as reception signals.
It is noted that, if the electrical waves are entered at the reception signal output terminal 104, the circularly polarized wave receiving antenna may be used as a circularly polarized wave generator for transmitting circularly polarized waves at the distal end of the waveguide 102 by the operation of synthesizer 105.
Also known in the field is a circularly polarized wave reception antenna made up of a reception unit 106 and a parabola-shaped reflector plate 108, as shown in FIGS. 5 and 6. The reception unit 106 is supported by the reflector plate 108 via a supporting bar 107. Further, the parabola-shaped reflector plate 108 is supported by the supporting shaft 109 so that the center axis of the concave portion thereof is aimed at, for example, a geostationary satellite.
The reception unit 106 includes a waveguide member 110 made up of a waveguide portion 110a and a cone-shaped field horn 110b connected to the distal end of the waveguide portion 110a, and a converter unit 112 attached to the waveguide member 110 via a substrate 111 fitted with the above-mentioned reception bar. The reception unit 106 is supported so that the field horn 110b is caused to face the parabola-shaped reflector plate 108. The field horn 110b is flared at its distal end, that is at the side of the parabola-shaped reflector plate 108.
Meanwhile, in the above-described circularly polarized wave generator and circularly polarized wave reception antenna, provided with the waveguide 102 and the dielectric plate 103, it is necessary for the dielectric plate 103 provided within the waveguide 102 to be of such a length as to produce a delay corresponding to 1/4.lambda. in the field amplitude components parallel to the major surface of the dielectric plate. The dielectric plate has its longitudinal direction parallel to the incident and/or radiating direction of the circularly polarized wave.
That is, the above-described circularly polarized wave generator and circularly polarized wave receiving antenna are of a stereo structure including both the incident and/or radiating direction for the circularly polarized wave and the direction perpendicular thereto so that it can not be reduced in size and thickness for providing a substantially planar structure. In addition, the dielectric plate 103 has to be mounted in position within the waveguide 102, thus complicating the structure and the production process.
On the other hand, in the above-described circularly polarized wave generator and the circularly polarized wave reception antenna, provided with the waveguide 102 and the synthesizer 105, it is necessary for the synthesizer 105 to have a transmission path of such a length as to cause a delay corresponding to 1/4.lambda. in one of the field amplitude components. The result is that, because of transmission losses at the synthesizer 105, it is difficult with the present circularly polarized wave generator and circularly polarized wave reception antenna to realize good reception and transmission characteristics, while it is difficult to reduce its size because of a larger space to be reserved for the synthesizer 105.